Electrical Properties of Quantum Dot Systems
Quantum dots, also denoted as artifical atoms or zero-dimensional electron systems, are objects where few to many electrons are confined in a small spatial enclosure of mesoscopic size (few tens to few hundreds of nanometers), allowing  a single electron only certain eigenvalues for its energy (‘quantum mechanical particle in a box’). more
Locally Probing Quantum Hall Samples
Measuring the Hall resistance on a two-dimensional charge carrier system at low magnetic fields allows determining the charge carrier concentration and the type of charge carrier (electron or hole). However at high magnetic field values (and low temperature), magnetic field intervals appear where the measured value is constant and well described by |RH|= h/ie2. more
Microscopic Picture of the Quantum Hall Effect
Scanning probe microscopy investigating quantum Hall samples has been performed in our group for many years and has led to a microscopic picture for the current distribution in quantum Hall samples which contradicts the current-carrying edge-state model. more
Hall Potential and Current Distribution in the Fractional Quantum Hall Regime
Recently, by using a scanning single-electron transistor microscope, we have measured the evolution of the Hall potential distribution versus magnetic field for several fractional quantum Hall regimes at temperature below 50 milliKelvin. Consistent with our previous results in the integer quantum Hall regime, in all cases we observe the same behavior, allowing us to extend our microscopic picture of the integer quantum Hall effect to the fractional quantum Hall effect. more
Magneto-Transport Measurements on Quantum Hall Samples: <br />Confirming the Microscopic Picture
In recent years we have done conventional magneto-transport measurements on various Hall bar samples demonstrating fingerprints of the edge- and bulk-dominated quantum Hall regime, confirming our microscopic picture which is based on dissipationless current flow in incompressible regions of the two-dimensional electron system. more
Array of Single-Electron Transistors on a Tip
Single-electron transistors are very sensitive electrometers which can easily detect even the presence of an electron or ion charge in its vicinity. We have developed a technique to fabricate a linear array of tips where on each tip a metal single-electron transistor is located. more
Hall sensors for Scanning Probe Applications
A Hall sensor tip, based on a (Al,Ga)As heterostructure, has been developed for use in a scanning probe microscope operated below 1 Kelvin. more
Scanning Probe Microscope operated below 0.1 Kelvin
In the last years, we have developed a scanning probe microscope operated in a 3He-4He dilution refrigerator below 0.1 Kelvin which uses single-electron transistors on a 1D tip array as locally probing electrometers. Hall potential profiles in the integer but also fractional quantum Hall regime have been measured. more
Two-Paths Quantum Hall Devices
Two-paths quantum Hall devices have been discussed in literature in terms of the edge-state picture as electronic interferometers. Our recent experimental investigations on a versatile mesoscopic quantum Hall device with in-situ tunable different combinations of parallel current paths shows in all combinations periodic conductance modulations in the applied magnetic flux. more
Supervelocities in Tunneling?
The transmission time tHa of an incident Gaussian wave packet through a barrier is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission velocity cHa = ℓ/tHa which appears under certain conditions as a supervelocity. more
Organic Electronics
The physics of organic solar cells und organic light emitting diodes has been explored in a common work with the company BASF SE in Ludwigshafen, Germany. more
Electron Beam Lithography
Within the Nanostructuring Lab, various substrates – conventional and unconventional – have to be structured by high resolution electron-beam lithography. The density and area size of the written pattern varies from application to application. Diverse resists have to be used, acting either as etching or lift-off mask. Facing a large variety of combinations, we have to challenge electron beam lithography. more
Nanostructuring Lab
With January 1st 2011, the cleanroom facility (previously a facility of the von Klitzing department) became part of the newly established Scientific Facility Nanostructuring Lab. Under class-10 cleanroom conditions with stable room humidity and temperature, samples can be processed by students of the Institute or in service by the cleanroom staff using photolithography, dry and wet etching, and material deposition under vacuum. more
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